1. Field of the Invention
The present invention relates to an antivibration device for a clutch pedal of a clutch operating mechanism.
2. Description of the Prior Art
In a hydraulic clutch operating mechanism, as publicly known, a clutch pedal is depressed by a driver to cause a hydraulic pressure in a master cylinder which actuates an operating cylinder to operate a withdrawal lever of a clutch. With such a hydraulic clutch operating mechanism, vibrations of an engine are propagated through the withdrawal lever to the operating cylinder. The thus propagated vibrations cause fluctuations (pulsations) in hydraulic pressure in the passage between the operating cylinder and the master cylinder, which in turn cause the clutch pedal connected to the master cylinder to vibrate. This vibration increases substantially in proportion to the engine revolutions. This problem is particularly acute in diesel engines which are likely to vibrate.
In order to solve this problem the passage communicating between the operating and master cylinders has been partially made of a readily expansible rubber hose to obtain a damping effect with the aid of the resilience of the rubber hose. In this case, however, the following disadvantages arise with the rubber hose approach to the problem.
(1) Since the expansive amounts of the rubber hose caused by hydraulic pressures are irregular, all the rubber hoses to be used must be selected through hydraulic pressure resistance tests which increases production costs.
(2) The rubber hose is apt to change in quality because it is in direct contact with the oil and exposed to the high temperature atmosphere in an engine compartment. Accordingly, the vibration damping capacity of the rubber hose is unstable.
(3) When an oil is introduced into the hydraulic passage, an air purge is needed in the passage. In air purging, the rubber hose is apt to collapse, which then results in a time-consuming and troublesome operation. Moreover, there is a tendency for air bubbles to stay in the passage, so that the air purge cannot be completely effected. The oil thus mixed with the air bubbles can cause troubles such as an incomplete disconnection of a clutch adapted to be operated by the oil.
(4) The inventors of this application have found in their experiments that the vibration damping effect using rubber hoses rapidly decreases at engine speeds higher than 2,500 rpm, beyond which speed effective antivibration for a clutch pedal cannot be effected.